Sensors have previously been coupled to cardiac leads. Since the leads are coupled to the myocardium they must possess flexibility and strength. If one or more electrodes are disposed distal to a sensor one or more electrical conductors must pass by the sensor thereby increasing the complexity of the sensor assembly and possibly increasing the dimension of the sensor package.
Since a sensor-bearing lead typically must be fixed in place within or on the heart for consistent sensed signals, an active fixation sub-assembly is often located at the distal tip. Given the closed distal tip and active fixation a stylet is oftentimes used to extend and retract a helical shaped member before torque is applied by a torque coil to fix the helix into adjacent tissue. Thus, the torque coil is a second elongated member, optionally electrically active, that must extend beyond the sensor. In the prior art the cables and coils were simply routed around the sensor module, or package.
For a number of reasons the sensor package of a physiologic sensor must be rendered electrically neutral. This has been accomplished with coating the sensor with insulating material(s) which are oftentimes of inconsistent depth and surface finish. Also, thermoplastic tubing has been used wherein a sensor package is surrounded in a uniform diameter tube of material and it is heat treated to shrink it around the package. This can also result in inconsistent material depth, air bubbles, and the like. Also, due to the thickness of these materials the material covering a transducer portion, such as a sensor membrane, had to be manually removed and replaced with another insulative material (after sealing the edges where the material was removed). Besides the excess time and complexity, the possibility that the numerical yield from this type of production technique can change (i.e., whether beginning at a reasonable yield the yield can vary or drop too low to predict or to make economic sense, respectively).
A need thus exists in the art for compact physiologic sensor packaging that allow stylet delivery, that can reliably convey electrical signals to and from the sensor as well as components coupled distal to the sensor, and that can easily, reliably, and efficiently be rendered electrically neutral (i.e., insulated).